Pitch trouble prevention method

ABSTRACT

There is provided an efficient pitch trouble prevention method in a papermaking step of paper production. The pitch trouble prevention method in a papermaking step of paper production includes: an aeration step of exposing at least one of white water and adjusted water to gas; and a pitch control agent addition step of adding a pitch control agent to at least one of the white water and the adjusted water.

TECHNICAL FIELD

The present invention relates to paper production, and more particularlyto a pitch trouble prevention method in a papermaking step of paperproduction.

BACKGROUND ART

Currently, paper production is performed through a papermaking step ofmaking paper from raw material slurry of pulp raw material dispersed inwater. In the papermaking step, a large amount of white water containingfine fiber and filler is discharged from a paper machine or the like.The discharged white water is circulated in the papermaking stepconsidering effective use and recycling of water resources.

However, since the white water contains pitch-generating substances suchas starch, sizing agent, latex, casein, or the like, circulating thewhite water tends to cause coagulation and coarsening of thepitch-generating substances. Also, the pitch-generating substances tendto be deposited on a bottom of a tank storing the white water, which mayalso cause coagulation and coarsening of the pitch-generating substancesin a deposit. When pitch generated by coarsening of the pitch-generatingsubstances is mixed into a product, the pitch causes trouble (pitchtrouble) such as reductions in product quality and productionefficiency.

Then, as a measure against the pitch trouble, in a white watercirculation system for circulating white water, part of the white wateris disposed of and new water is introduced to avoid concentration ofpitch-generating substances, which does not solve the problem alone.

As a further measure against the pitch trouble, a method of adding apitch control agent to a white water circulation system has beenproposed (for example, see PTL 1). The pitch control agent is effectivefor pitch suspended in water and useful for reducing the pitch.

However, it has been found that the pitch control agent is not veryeffective for pitch in a deposit on a bottom of a tank, and cannot exerta sufficient effect on coarsened pitch. Then, to reduce such kinds ofpitch, a large amount of pitch control agents needs to be added.However, the pitch control agent is relatively expensive, and areduction in usage of the pitch control agent is desired to reduceeconomic burden.

REFERENCE LIST Patent Literature

PTL1: JP 2014-141774 A

SUMMARY OF INVENTION Technical Problem

The present invention is achieved in view of such circumstances, and hasan object to provide an efficient pitch trouble prevention method in apapermaking step of paper production.

Solution to Problem

To achieve the object, the present inventors have diligently studied andfound that at least one of a white water circulation system and anadjusted water system is exposed to gas, and a pitch control agent isadded to at least one of the white water circulation system and theadjusted water system, thereby efficiently suppressing coagulation ofpitch to prevent pitch trouble.

Specifically, the present invention provides [1] to [4] described below.

[1] A pitch trouble prevention method in a papermaking step of paperproduction including: an aeration step of exposing at least one of awhite water circulation system and an adjusted water system to gas; anda pitch control agent addition step of adding a pitch control agent toat least one of the white water circulation system and the adjustedwater system.

[2] The pitch trouble prevention method of [1], wherein the pitchcontrol agent addition step is performed after the aeration step.

[3] The pitch trouble prevention method of [1] or [2], wherein in thepitch control agent addition step, an amount of the pitch control agentto be added is 0.1 mg/L to 10,000 mg/L per kg of suspended solids.

[4] The pitch trouble prevention method of any of [1] to [3], wherein inthe aeration step, an aeration tank having a diffuser at a bottom isused, and an amount of aeration by the diffuser is 0.5 m³/h to 10 m³/hper m² of bottom area of the aeration tank.

[5] The pitch trouble prevention method of any of [1] to [4], wherein inthe aeration step, both the white water and the adjusted water areexposed to gas.

[6] The pitch trouble prevention method of any of [1] to [5], wherein atime from the aeration to the addition of the pitch control agent is 0to 30 minutes.

Advantageous Effects of Invention

According to the present invention, an efficient pitch troubleprevention method in a papermaking step of paper production can beprovided.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 shows one aspect of a papermaking step according to an embodimentof the present invention.

DESCRIPTION OF EMBODIMENT

A pitch trouble prevention method in a papermaking step of paperproduction according to an embodiment of the present invention includes:an aeration step of exposing at least one of white water and adjustedwater to gas; and a pitch control agent addition step of adding a pitchcontrol agent to at least one of the white water and the adjusted water.

[Papermaking Step]

A papermaking step of paper production will be described. FIG. 1 showsone aspect of a papermaking step according to an embodiment of thepresent invention.

In the papermaking step, raw material pulp slurry produced in a rawmaterial production step 1 and stored in a machine tank 2 is fed bypumps 3, 27 through a screen 4 to an inlet 5. The raw material pulpslurry fed to the inlet 5 is supplied to a wire part 6 and dehydrated. Adehydrated wet sheet 7 is fed through a press part 8 to a dryer part 9.

A liquid separated by the wire part 6 is white water 10. The white water10 usually contains fine fiber from raw material pulp used inpapermaking, or other chemical agents for paper production.

The white water 10 separated by the wire part 6 is stored in a whitewater silo 11. The white water stored in the white water silo 11 may beexposed to air (gas), or a pitch control agent 12 may be add thereto.The white water stored in the white water silo 11 is supplied to the rawmaterial pulp slurry as long as the concentration or the like of thewhite water satisfies the condition of papermaking. The white waterstored in the white water silo 11 and which does not satisfy thecondition of papermaking is fed by a pump 23 to an aeration tank 13 andstored. The white water stored in the aeration tank 13 may be exposed toair (gas), or a pitch control agent 14 may be add thereto. The whitewater from the aeration tank 13 is fed by a pump 25 to a solid-liquidseparator 15. Part of the white water fed to the solid-liquid separator15 is fed to an aeration tank 17 and stored. From the rest of the whitewater fed to the solid-liquid separator 15, solids are discharged orcollected by a raw material system (16).

The white water stored in the aeration tank 17 may be exposed to air(gas), or a pitch control agent 18 may be add thereto. The white waterfrom the aeration tank 17 is supplied downstream of the machine tank 2by a pump 26, and mixed with the raw material pulp slurry. The rawmaterial pulp slurry mixed with the white water is fed by the pumps 3,27 through the screen 4 to the inlet 5 as described above.

A system for circulating the white water described so far is a whitewater circulation system 22.

In the white water circulation system 22, aeration processing of thewhite water or pitch control agent addition processing to the whitewater is preferably performed in at least one of the white water silo 11and the aeration tanks 13, 17 storing the white water (dilution water),and any number of the white water silo 11 and the aeration tanks 13, 17may be provided. In the white water circulation system 22, the aerationprocessing of the white water or the pitch control agent additionprocessing to the white water is more preferably performed in the whitewater silo 11 considering that the pitch control agent can besufficiently mixed with the raw material pulp slurry.

In the white water circulation system 22, the aeration processing of thewhite water or the pitch control agent addition processing to the whitewater may be performed in the machine tank 2 or the like storing the rawmaterial pulp slurry, and is more preferably performed in the machinetank 2 or the like storing the raw material pulp slurry in addition tobeing performed at the places where the white water (dilution water) isstored. Raw material dilution water containing the white water isexposed to air (gas) or the pitch control agent is added thereto,thereby enhancing an effect of the pitch control agent on the entirewhite water circulated in the white water circulation system 22.

In the white water circulation system 22, adjusted water may be suppliedfrom an adjusted water system 19 to adjust the concentration of thecirculated white water. The adjusted water may include, but not limitedto, for example, soft water and hard water for paper production.

The adjusted water from the adjusted water system 19 may be exposed toair (gas) in an aeration tank 20, or a pitch control agent 21 may beadded thereto. The adjusted water from the aeration tank 20 is fed by apump 24 to the aeration tank 13 to adjust the concentration of the whitewater.

The white water and the adjusted water may each contain a small amountof chemical agent for paper production without reducing the effect ofthe present invention.

Examples of the chemical agent for paper production may include, but notlimited to surfactant, wax, sizing agent, filler, anti-corrosive agent,conductive agent, anti-foaming agent, slime control agent, dispersant,viscosity modifier, flocculant, coagulant, paper strengthening agent,retention aid, paper powder falling preventing agent, and bulking agent.

Examples of the raw material pulp used for papermaking may include, butnot limited to chemical pulp, mechanical pulp, and waste paper pulp.

Examples of the chemical pulp may include leaf bleached kraft pulp(LBKP), needle bleached kraft pulp (NBKP), leaf unbleached kraft pulp(LUKP), and needle unbleached kraft pulp (NUKP).

Examples of the mechanical pulp may include ground pulp (GP),thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), andrefiner mechanical pulp (RMP).

Examples of the waste paper pulp may include waste corrugated boardpulp, waste liner pulp, waste magazine pulp, waste newspaper pulp, wasteland certificate pulp, waste high grade white paper pulp, and deinkedwaste paper pulp.

[Aeration Step]

In an aeration step, at least one of the white water and the adjustedwater is exposed to gas. The aeration refers to supplying gas to thewhite water and the adjusted water.

In the aeration step, both the white water and the adjusted water arepreferably exposed to gas considering that the gas can be sufficientlysupplied to the white water and the adjusted water and that pitchcoagulation in the entire white water circulation system can be easilysuppressed to prevent pitch trouble.

In the aeration step, the white water after separated by the wire part 6and before mixed with the raw material pulp slurry is preferably exposedto gas considering that pitch coagulation in the white water circulationsystem can be easily suppressed to prevent pitch trouble.

Examples of the gas used for aeration may include, but not limited to, amixed gas and a high purity gas. The gas used for aeration is preferablya mixed gas, more preferably an oxygen-containing gas, and furtherpreferably air considering its availability. The oxygen-containing gascontains, besides oxygen, nitrogen, carbon dioxide, and the like. Theoxygen-containing gas may be used alone, or two or more kinds ofoxygen-containing gases may be used in combination.

An aeration method may be any method that can supply gas to at least oneof the white water and the adjusted water. The aeration method may use,for example, a diffuser and agitation. In particular, a method using adiffuser such as a diffuser pipe and a diffuser plate is preferableconsidering stable and continuous aeration. As a specific method using adiffuser, a diffuser can be provided at a bottom of a tank to blowmicrobubbles upward from the bottom, thereby increasing contactefficiency of target water and gas to perform efficient aeration.

The diffuser may have, but not limited to, for example, an opening witha diameter of 1 mm to 5 mm at a predetermined interval of 5 cm to 50 cm.One or more diffusers may be provided.

In the white water circulation system and the adjusted water system,aeration may be performed in any position such as in an aeration tank, apipe, or a channel. The aeration is preferably performed in the aerationtank considering more efficient aeration in a large scale. The aerationtank preferably has a diffuser at a bottom. The aeration tank may haveany shape such as a box shape, a circular shape, an elliptical shape, ora bowl shape. One or more aeration tanks may be provided in the whitewater circulation system and the adjusted water system.

In the aeration step, it is preferable that the aeration tank having adiffuser at a bottom is used, and an amount of aeration by the diffuseris preferably 0.5 m³/h to 10 m³/h per m² of bottom area of the aerationtank. The amount of aeration within the above range allows the gas to besufficiently supplied to the white water and adjusted water. Consideringthe above and a reduction in production cost, the amount of aeration ismore preferably 1.0 m³/h to 9.0 m³/h, and further preferably 1.5 m³/h to8.0 m³/h per m² of bottom area of the aeration tank.

An aeration time in the aeration step may be, but not limited to,preferably 3 minutes to 30 days, more preferably 4 minutes to 20 days,and further preferably 5 minutes to 10 days. The aeration time withinthe above range reduces production cost and allows the gas to besufficiently supplied to the white water and the adjusted water. Theaeration may be performed continuously or several times.

[Pitch Control Agent Addition Step]

In a pitch control agent addition step, the pitch control agent is addedto efficiently suppress pitch coagulation and then prevent pitchtrouble.

In the pitch control agent addition step, both the white water and theadjusted water are preferably exposed to gas considering that pitchcoagulation in the entire white water circulation system can beefficiently suppressed to prevent pitch trouble.

In the pitch control agent addition step, the pitch control agent ispreferably added to at least the adjusted water considering that thepitch control agent can be added to a small amount of water andefficiently mixed with the white water to exert an effect of the pitchcontrol agent on the entire white water circulation system from arelationship between an amount of water in the white water circulationsystem and an amount of water in the adjusted water system.

Examples of the pitch control agent may include, but not limited to,surfactant, polymer, inorganic material, organic compound, oil content,starch, protein, enzyme, cyclodextrin, water-soluble cellulose,emulsifier, oxidant, and chelator.

Examples of the surfactant may include cationic surfactant, anionicsurfactant, and non-ionic surfactant.

Examples of the polymer may include water-soluble polymer, cationicpolymer, anionic polymer, ampholytic polymer, and non-ionic polymer.Examples of the polymer may include quaternary ammonium polymer, esterpolymer, ether polymer, alcohol polymer, glycol polymer, ether esterpolymer, methacrylic polymer, amide polymer, amine polymer, endocyclicnitrogen compound, polyvinyl alcohol, polyamide, polyetherester amide,polyethylenimine, polyamine/epihalohydrin, hydroxyalkyl cellulose,modified silicone, phenol resin, polyvinyl acetal resin, melamine resin,urethane resin, and poloxamer. Examples of the amide may includeacrylamide. Examples of the amine may include alkylamine,alkylenediamine, and diallylamine.

Examples of the inorganic material may include alkali metal salt,aluminum compound, iron compound, calcium compound, talc, bentonite,zeolite, diatom earth, mica, white carbon, and inorganic acid.

Examples of the organic compound may include organic acid and alcohol.Examples of the organic acid may include phosphonic acid, gluconic acid,malic acid, citric acid, acetic acid, sulfonic acid, maleic acid,tartaric acid, lactic acid, and glycolic acid. Examples of the alcoholmay include terpene alcohol. Examples of the endocyclic nitrogencompound may include pyrrolidone.

Examples of the oil content may include wax, mineral oil, vegetable oil,and animal oil.

The pitch control agent is commercially available from KURITA WATERINDUSTRIES LTD. under the product name “Spanplus”.

The pitch control agent may be used alone, or two or more kinds of pitchcontrol agents may be used in combination.

An amount of the pitch control agent to be added is, but not limited to,preferably 0.1 mg/L to 10,000 mg/L per kg of suspended solids (SS). Theamount of the pitch control agent to be added within the above rangeallows the pitch control agent to exert a sufficient effect on pitch.Considering the above, the amount of the pitch control agent to be addedis more preferably 5.0 mg/L to 5,000 mg/L, and further preferably 50mg/L to 1,000 mg/L per kg of SS.

The pitch control agent may be added once or in several portions.

The pitch control agent addition step is preferably performed after theaeration step. Adding the pitch control agent after the aeration stepallows the pitch control agent to exert a sufficient effect on pitch ina deposit on the bottom of the tank and coarsened pitch. Specifically,the above order of steps can efficiently suppress pitch coagulation inthe white water circulation system, and can exert a sufficient effect oncoarsened pitch, thereby preventing pitch trouble.

A time from the aeration processing to the addition of the pitch controlagent is not limited as long as an effect of the aeration lasts, and ispreferably 0 to 30 minutes, more preferably 0 to 25 minutes, and furtherpreferably 0 to 20 minutes.

The pitch trouble prevention method according to the embodiment of thepresent invention can expose at least one of the white water and theadjusted water to gas, and can add the pitch control agent to at leastone of the white water and the adjusted water, thereby efficientlysuppressing pitch coagulation to prevent pitch trouble.

The pitch trouble prevention method according to the embodiment of thepresent invention can reduce or optimize usage of the pitch controlagent as compared to a case without aeration. This may be because thegas increases fluidity in the tank to physically suppress bonding of thehydrophobic group of pitch-generating substances. Further, although thedeposit on the bottom of the tank decomposes and organic acid producedby a microorganism and calcium bond to generate pitch of fatty acidcalcium salt, circulation by the aeration can remove the deposit andprevent decomposition, thereby suppressing generation of pitch of fattyacid calcium salt.

EXAMPLES

Next, the present invention will be described in more detail withexamples, but the present invention is not limited by the examples.

A testing method of a test sample will be described below.

<Redox Potential (ORP)>

Redox potential (mV) was measured using a redox potential meter withpotentiometry (manufactured by Toko Chemicals Inc.).

<Pitch Amount and Pitch Particle Size>

A pitch amount (μm³) and a pitch particle size (μm) were measured by amethod described in JP 6222173 B. Specifically, a fluorescent dye wasadded to a test sample, pulp slurry containing dyed pitch was observedthrough a fluorescence microscope under the conditions described below,and an image thereof was taken by a CCD camera. The obtained image wasanalyzed by image analysis software (manufactured by MITANI CORPORATION,product name “WinROOF”) to measure a pitch amount and a pitch particlesize.

Microscope: fluorescence mirror unit: manufactured by OlympusCorporation, product name “U-FBW”

Fluorescence source: halogen lamp: manufactured by Olympus Corporation,product name “U-HG LGPS”

CCD camera: manufactured by Olympus Corporation, product name“DP73-SET-A”

Eyepiece: 10×

Objective Lens: 10×

Shutter speed: 1 second

Field stop, aperture stop: both open

Intensity of halogen lamp: 3

Image size: 1200×1600 pixels

Example 1

White water separated by a paper machine (wire part) in a certain papermill was obtained and used as a test sample. An SS content in the testsample was 0.312%. A pitch amount in the test sample was 803 μm³, and apitch particle size was 0.265 μm.

The test sample was subjected to aeration processing and pitch controlagent addition processing described below.

<Aeration Processing>

Gas: air gas

Aeration tank: with a diffuser (diffuser pipe having an opening of 2 mmat an interval of 10 cm) at a bottom

Amount of aeration: 2 m³/h per m² of bottom area of the aeration tank

<Pitch Control Agent Addition Processing>

Pitch control agent: product name “Spanplus 500” (manufactured by KURITAWATER INDUSTRIES LTD.)

Addition amount: 400 mg/L per kg of SS

Comparative Example 1

The test sample was subjected to only the above mentioned aerationprocessing.

Comparative Example 2

The test sample was subjected to only the above mentioned pitch controlagent addition processing.

TABLE 1 Pitch Pitch Pitch ORP amount particle size trouble (mV) (μm³)(μm) (%) Example 1 153 148 1.53 70 Comparative 153 510 2.26 100 example1 Comparative −400 448 1.55 80 example 2

In Comparative example 1 in which the aeration was performed using theoxygen-containing gas, an increase in ORP (suppression of decomposition)and a reduction in deposit on a bottom of a tank were confirmed ascompared to Comparative example 2 in which the processing using only thepitch control agent was performed.

In Comparative example 2 in which the processing using only the pitchcontrol agent was performed, reductions in pitch amount and pitchparticle size were confirmed, but decomposition in the deposit on thebottom of the tank was not able to be suppressed as compared toComparative example 1.

On the other hand, in Example 1 in which both the aeration using the gasand the addition of the pitch control agent were performed, an increasein ORP (suppression of decomposition), removal of the deposit, andreductions in pitch amount and pitch particle size in a system wereconfirmed. Thus, a reduction in pitch trouble to 70% was confirmed ascompared to pitch trouble (defect due to pitch) of 100% in conventionalcases.

INDUSTRIAL APPLICABILITY

The pitch trouble prevention method of the present invention caneffectively suppress and prevent pitch trouble such as a paper spot, apaper defect, a paper break, a reduction in workability in a papermakingstep of paper production.

REFERENCE SIGNS LIST

-   -   1 raw material production process    -   2 machine tank    -   3 pump    -   4 screen    -   5 inlet    -   6 wire part    -   7 wet sheet    -   8 press part    -   9 dryer part    -   10 white water    -   11 white water silo    -   12 pitch control agent    -   13 aeration tank    -   14 pitch control agent    -   15 solid-liquid separator    -   16 solids are discharged or collected by raw material system    -   17 aeration tank    -   18 pitch control agent    -   19 adjusted water system    -   20 aeration tank    -   21 pitch control agent    -   22 white water circulation system    -   23 pump    -   24 pump    -   25 pump    -   26 pump    -   27 pump

1. A pitch trouble prevention method in a papermaking step of paperproduction, comprising: an aeration step of exposing at least one ofwhite water and adjusted water to gas; and a pitch control agentaddition step of adding a pitch control agent to at least one of thewhite water and the adjusted water.
 2. The pitch trouble preventionmethod according to claim 1, wherein the pitch control agent additionstep is performed after the aeration step.
 3. The pitch troubleprevention method according to claim 1, wherein in the pitch controlagent addition step, an amount of the pitch control agent to be added is0.1 mg/L to 10,000 mg/L per kg of suspended solids.
 4. The pitch troubleprevention method according to claim 1, wherein in the aeration step, anaeration tank having a diffuser at a bottom is used, and an amount ofaeration by the diffuser is 0.5 m³/h to 10 m³/h per m² of bottom area ofthe aeration tank.
 5. The pitch trouble prevention method according toclaim 1, wherein in the aeration step, both the white water and theadjusted water are exposed to gas.
 6. The pitch trouble preventionmethod according to claim 1, wherein a time from the aeration to theaddition of the pitch control agent is 0 to 30 minutes.